This invention relates to novel arrangements for manipulating electromagnetic actuator systems.
Magnetic disk files for recording and storing data are widely used in data processing; e.g., as peripheral memory. Disk files have the advantage of facilitating data transfer at randomly selected address locations (tracks) and without need for the "serial seek" mode characteristic of magnetic tape memories.
As workers are aware, the transducers used in association with disk recording surfaces must be reciprocated very rapidly between selected address locations (tracks) with high precision. It will be recognized as important for such a system to move a transducer very rapidly between data locations; and to do so with high positional accuracy between closely-spaced track addresses. This constraint becomes very tricky as track density increases--as is presently the case. Typically, such disk storage systems mount the transducer head on an arm carried by a block that is supported by a carriage. This carriage is usually mounted on track ways for reciprocation by an associated transducer actuator.
Workers will recognize that the present trend is toward ever higher track density with increased storage capacity and decreased access time. Of course, as track density rises, closer control over the actuator mechanism is necessary to position transducer heads accurately over any selected track, lest signals be recorded, or read, with too much distortion, and without proper amplitude control, etc.
Known Positioners:
Such transducer actuators (linear positioners) employed with magnetic disk memory systems are subject to stringent requirements; for instance, these systems typically involve a stack of several magnetic disks, each with many hundreds of concentric recording tracks spanning a radius of about 12 inches; and a head-carrying arm is typically provided to access each pair of opposing disk surfaces. This arm will typically carry two to four heads so that it need be moved only about 3 inches (radially) to position its heads adjacent any selected track. Thus, it will be appreciated that such applications involve extreme positioning accuracy together with very high translation speeds (to minimize access time--a significant portion of which is used for head positioning). Such a positioner must move its transducer heads very rapidly so that the associated computer can process data as fast as possible--computer time being so expensive that any significant delay over an extended period (of even a fraction of a millisecond) can raise costs enormously ("transition time", during which heads are moved from track to track, is "dead time" insofar as data processing is concerned, of course). Thus, computer manufacturers typically set specifications that require such inter-track movements to take no more than a few milliseconds. Such high speed translation imposes extreme design requirements: it postulates a powerful motor of relatively low mass (including carriage weight) and low translational friction.
Another requirement for such head positioners is that they exhibit a relatively long stroke, on the order of 1-4 inches or more, in order to minimize the number of heads required per recording surface [pair].
The prior art discloses many such positioner devices, including some intended for use in magnetic disk memory systems: e.g., see U.S. Pat. Nos. 3,135,880; 3,314,057; 3,619,673; 3,922,720; 4,001,889; 4,150,407; 3,544,980; 3,646,536; 3,665,433; 3,666,977; 3,827,081; and 3,922,718 among others.
Among prior art approaches are the "Head-per-Track" approach whereby (some or all) disk faces, or pair thereof, are provided with a head which is "dedicated" to a respective track. This will be contrasted with the more usual "movable head" systems, which may be used alone, or with such a "Head-per-Track" arrangement; the latter here covering some of the tracks in some or all of the disk faces.
Workers recall that such actuator carriages are driven by various actuator mechanisms, including the well known "voice coil" motor (VCM, comprising a solenoid like those used to drive an audio speaker). Such are explained in my cited copending U.S. Ser. No. 106,847, as are various "flat-coil" actuators according to a feature hereof.
FIG. 26 shows a simplified view of a prior art disk pack D-D understood as comprising an array of like recording disks mounted to be co-rotated on a common spindle and spaced uniformly therealong, each disk having a pair of recording faces with a plurality of concentric recording track sites (tr) and being accessible by read/write transducer such as those indicated. The indicated transducers are mounted in pairs from a common axis arm with a plurality of arms projecting in common from a single transducer actuator TA adapted to reciprocate the arms in common to position one of the given heads above an associated selected track site as well known in the art.
A disk drive (DD) will be understood conventionally as a mechanism that holds several magnetic disks, keeps them spinning, and moves the read/write heads into position when information must be read from, or stored on, one of the disks. One presently popular form of DD technology, the "Winchester", is viewed as highly reliable by today's standards, yet has a mean time between failure (MTBF) of from 8,000-12,000 hours (see April 1981 Edition of Output Magazine, pages 24,25). The cited article mentions that the principle drawback for such technology (or for any form of "on-line mass memory") is "the lack of a secure backup system" raising the equation: How can a user protect against loss of (much or all of) a data base if his on-line memory is damaged by machine malfunction, by programming or operator error, by fire or any similar calamity?
It is acknowledged that the excellent MTBF's of present (Winchester) technology offers a high degree of reassurance--but it is just not high enough for many users of DD memory who are troubled by the likelihood of "Hard" failure at 8,000-12,000 hours. Thus many workers now ponder how to secure a suitable backup. One suggestion is a backup system based on floppy disks; another is based on "Streaming" tape drives (which run continuously instead of in the conventional start-stop fashion); another are data cartridges or video cassettes. All these backup systems are typically more expensive then users care to indulge these days and (e.g., in the case of floppies) will very seriously degrade the operation of the DD unit.
"Dual Path to Data" concept:
A salient feature of this invention involves modifying a typical disk drive arrangement (e.g., like that above mentioned) so as to exhibit a "dual path to data" capability, analogous to (actually) having a plurality of head-actuator units available to provide "overlapping coverage" to (some or all) of the tracks in each disk stack. Thus, for instance, with each pair of disk faces having a related pair of transducer-actuator units available to access both faces, failure of any one unit can automatically invoke the substitution of the other unit.
Similarly, each such actuator unit in the pair may include a similar control stage so that failure of one control stage can automatically invoke substitution of the other compensatorily. Thus, as further explained below, workers will appreciate that a "dual path to data" capability can be afforded either by multiple transducer actuators giving "overlapping coverage" or by multiple actuator controls which are "cross-switchable", or both implementations where feasible. It is an object to teach this.
"Cross-switchable" actuator controls:
For a simplistic showing of such a multiple actuator control arrangement please note FIGS. 21, 22 and 23, (described below in detail) where failure of one control unit is understood to automatically invoke a "substitution sequence" calling in the companion control unit and thus keeping the system "on the air".
"Overlapping-coverage" by multiple transducer units:
FIGS. 1A and 24 (described below in detail) schematically indicate the other approach whereby (selected) record faces are given "overlapping coverage" by a plurality (two are shown) of transducer actuator arrays, and to be cooperatively controlled and manipulated to afford such a "dual path to data" feature. That is, if one actuator unit fails, its companion unit may be called in to "cover" for it (i.e. to service the tracks primarily assigned to the failed unit).
Vulnerability to failure of typical disk drive; (FIG. 25):
Workers in the art of designing, making and/or using EDP systems are acutely sensitive to the problem of "catastrophic system failure" or "Hard" failure, where for some reason an entire EDP system or subsystem becomes essentially inoperative for a significant time. While an entire system is thus "off the air" some very bad things begin to happen: People in the user establishment typically rely very heavily on the EDP system (and it is typically too expensive to afford redundancy whereby a "standby system" is available for substitution--except in the case of a few ultra-large installations). Extreme pressure is brought to bear on the user's people every second the system is "down".
These people in turn very quickly make the system's vendor (sales people, leasing agent and associated manufacturing people) acutely aware of how unpleasant their life has suddenly become. A parallel pressure is applied to the purveyor's management because of the loss of leasing revenue or the possibility of a system "return", loss of future sales, etc. Thus everyone concerned with an EDP system will go to enormous lengths to keep it "on the air", even if this means it might "limp along" for a time at reduced effectiveness (e.g., operating at reduced speed) this being known in the art as "Soft" failure.
Now the disk drive (DD) components in such an EDP system are typically the most critical (present the greatest risk) viz a viz such a "Hard" failure of the entire system. This is because a DD unit is so used that it is usually "ON-Line" and it is not feasible to "bypass" it if it fails (unlike other different components, such as tape drives, card readers or printers, etc., which can themselves "go down" without dragging the whole EDP system down with them--this is partly because such input and output devices do not typically operate "on-line" with the CPU and in "real time", whereas a DD unit often does; thus if such off-line I/O unit fails, the system CPU may "busy itself", at least temporarily, by turning to other tasks; but this is not possible with a DD which typically may be the only "data-bridge" between the CPU and the outside world, spending much of its operating life linked "on-line" into the "data-paths" of the CPU while the CPU is manipulating and temporarily storing data; thus "Hard" failure of the DD unit by analogy "blows a fuse" in the on-line "data-path" of the CPU and so shuts down the entire system).
Illustrative processing cycle of an EDP system, DD failure:
An illustration may help clarify things. FIG. 25 is intended to very schematically and functionally depict such a typical EDP system with a pair of host central processors (CUP-1,-2) surrounded by clusters of servient peripheral units such as the array of card readers, CR, the array of cathod ray terminals CRT (typically with a keyboard for communicating to a CPU) an array of high speed printer units, PR, an array of tape drives, T, an array of Key-to-tape units KT, an array of optical reader units RP, an array of phone line connections, or modems, TM, and several disk drive units DD. The system is very sketchily shown, of course, but it will be understood as operating according to present good state-of-the-art practice.
Briefly recounting a typical operating day for this EDP system in FIG. 25 may be instructive, assuming the system is used in a large commercial bank, for example. During business hours, system operators will typically keep the CPUs busy, e.g., access either to provide current business information to management or to customers such as a daily summary of the latest status of bank finances and those of major customers or similar summary reports to large customers on the state of their accounts (e.g., to minimize their "float" and maximize profits on the use of their money). Also they may answer specific real-time queries of bank management or customers (e.g., a new customer wants a very large loan for 10 days: Can the bank swing it?--or the creditor of a customer inquires after his credit status, payment record, etc.). For instance, in a time-sharing mode, the two CP units might be capable of handling questions from 10 CRT units and several modem terminals, while also plugging-in and -out with one of the DD units in the course of answering questions and manipulating data. During the day company business and customer account changes typically involve a massive real time traffic demands on the system.
For this reason other, less pressing tasks are deferred; e.g., such tasks as updating accounts, receiving reports from satellite bank branches reconciling debits and credits for the whole bank network to arrive at an accurate overall balance. These tasks are relegated to the non-business hours (e.g., late evening) when the CP units are not otherwise busy--then the CP may attend to these and other "housekeeping" duties.
Thus, during the evening, input is received from branch banks and customers, etc.; e.g., being provided through the telephone modem units (perhaps being stored temporarily on a DD for fast transmission off the wire, then later dumped at a slower rate into tape drive units). Night workers may feed in results from the day's mail and from the day's transaction receipts (e.g., via card reader units CR or Key-to-tape) and these may be fed to similar slow-speed archival memory (tape drive). The CP units may then, in their own good time, call-up such input data once it has been fully received, organized and stored in local memory, doing this at the usual fast efficient rate (e.g., when the CP is ready to summarize the day's transactions or to begin updating customer accounts, etc.). Just before this, it will direct the appropriate tape drive to make a memory dump to a specific DD, the CPU keeping busy meanwhile on other things during the slow-speed dump--and later turning to the DD for high-speed data interchange in "real time". As workers know, it is more efficient for a CP to talk to a DD with the usual "fast data rate" then to a much slower, serially-organized tape drive--hence the TD uses the DD as its "middleman".
In this manner, all the input data for the previous business day may be digested and stored in the system, with accounts reconciled and status reports prepared (printed) prior to the beginning of the next day's business day.
Workers will recognize that in all these typical system operations the DD is the only peripheral unit that is so co-operative with the CP units operation in real time that it can actually "pull down" the CPU if it fails. That is, if a CP unit is working on a given block of data temporarily stored on a given DD and the DD fails during some manipulating sequence (e.g., while figuring a certain payroll--with all the hours, rates, latest deductions, etc., etc., stored on the DD for real-time use by the CP) this DD-failure will typically block further operation (on this sequence at least) by the CP. Of course in certain instances it may be possible for the CP to abort the entire sequence and start anew with a second DD unit, but this would mean an extravagant waste of time and money and few operations allow for this.
Objects:
Thus, I have discovered that preventing "Hard failure" of a DD unit is especially critical to operation of an entire EDP system. (Presently workers say that DD failure accounts for almost all of the urgent service calls to an EDP site). Accordingly, by this invention, I have addressed the problem of DD Hard failure and attempted to ameliorate this, converting it to a "Soft" failure to the obvious benefit of an entire associated EDP system.
I have learned that DD failure is very often due to failure of a motor; less often because of a head crash; even less often due to failure of the actuator or the head electronics, (as workers know, once any head impacts a disk in a typical fixed DD all the other heads will "crash" against their confronting disk, gouging the disk and themselves, and of course destroying data in the process). Indeed I have found that the DD units are the most prone to serious failure of a type which interrupts the overall EDP system and "brings it down", resulting in expensive down-time and service calls. Here, I address the problem of DD failure and associated blockage of a "DP path" in an EDP system, and attempt to alleviate this by providing for "soft-failure" of a DD unit via a "multi-path to data" capability. That is, this approach focuses on the criticality of head-actuator units and provides "alternate paths to data", at least for all critical tracks in a disk file. A preferred way is to do so by providing alternative modes of "soft-failure" for the head actuator portions of a disk file.
One preferred soft failure results from providing a novel "cross-bar" arrangement between a plurality of like head actuator arrays serving a common disk file whereby the electronic-control stage for each array is connected to be "cross-coupled" to one or several other arrays for emergency servicing thereof.
"Soft-failure": is also here taught as implemented by providing a plurality of head-actuator units for all (critical) tracks, these units having a capability for overlapping track coverage, in case of emergency. That is, this "multi-path to data" approach provides two or more transducer units for each recording disk face, or pair of faces. The above mentioned flat coil actuator design will be seen to facilitate this. This may be optimized by apportioning transducer coverage across each given disk face and providing for "emergency mode" overlapping coverage by adjacent transducer units.
Multiple overlapping transducer coverage; Ex. I:
An Example of this multiple overlapping transducer coverage may be understood as follows with a given conventional Fixed Disk Drive with the disk file thereof presenting like disk recording faces, each with 1,000 tracks and with three (3) associated transducer arrays: array i, array ii and array iii. Each array is conventionally adapted to be translated radially to a selected track in its associated track set. Array i is assigned to normally cover a first group of tracks, namely outermost tracks 1-100, these being the most frequently used; array ii is assigned to normally cover tracks 101-300, the next most "popular" tracks; array iii is assigned to cover the rest: namely tracks 301-1000. Each transducer array will, according to this invention, be adapted to also cover the adjacent track span in a prescribed "emergency mode" of operation. In this emergency mode, for example, if transducer array i fails for any reason, the adjacent array ii can be (automatically) thrown into emergency mode and operated to cover the tracks of array i (i.e., tracks 1-100) as well as its regularly assigned span.
Similarly, if the array ii goes down, either adjacent array i and/or array iii can be thrown into emergency mode to cover its track span (#101-300) and so forth. This characterizes this kind of "Soft failure" capability (as well as a "multi-path to data" or "overlapping transducer coverage") since the failure of any one transducer array does not cause catastrophic failure of the DD unit or of the associated EDP system. Rather it merely throws the DD into an emergency mode which will characteristically operate a bit slower and less efficiently but nonetheless keep the entire EDP system "on the air"--something very desparately desired in the art now as workers know.
Similarly, in certain operating modes, such a "multiple overlapping transducer coverage" can be advantageously used in regular, non-emergency operations. For instance, to reduce access time and improve DD performance. That is, the hardware and software can be arranged in such a DD so that while any one transducer array (array i) is operating on a given assigned track (e.g., #11) and where the "next track up" (e.g., #91) happens to lie in the same span of tracks (e.g., #1-100) covered by this "busy" array, the system will turn to the adjacent transducer (array ii) invoking an "assist mode" and, translating it to that track, to service it as soon as the first array i is finished (with track #11; e.g., while the "busy" transducer i is awaiting completion of a disk revolution, as it sometimes must). This second transducer will now be used, rather than the first, to operate on this "next-up" track. Workers in the art will appreciate how such multiple track coverage and how such anticipation of "translation time" can reduce access time, since translation time is the biggest obstacle to fast access in a DD unit. Other variants of this "assist mode" and overlapping transducer coverage will be appreciated by those skilled in the art.
"Cross-bar" feature:
Another related implementation of the "multi-path to data" capability involves such a system having a plurality of transducers per disk file (stack), each with associated control means, wherein a control means for one transducer unit may be switched to operate another unit in the file--e.g., where one control unit fails, the associated transducer may still be operated (albeit somewhat slower) perhaps while awaiting field repair; the system thus going "fail-soft" and not going down completely! To this end the control means are inter-coupled with "cross-bar" means allowing them to be so switched.
Workers will see that this implementation can even be used to dispense with the abovementioned redundant transducer coverage or overlapping transducers while yet keeping many of its salient advantages. That is, it may be preferable to use the overlapping multiple transducer feature together with this "cross-bar" coupling control unit;--however, it will be apparent that for a cost-reduced DD one may dispense with the overlapping, while yet still achieving "Soft-failure" and multi-path to data capability by just cross-coupling the actuator control units, (for instance, as indicated in FIG. 23, further described below). With this feature, the DD will "Fail-soft" and keep the system on the air when one of several head actuator control units fails. Of course, this "cross-coupling" of control stages (cross-bar feature) is preferably used together with the multiple actuator per face implementation for a more comprehensive fail-soft capability.
Thus, one object of this invention is to provide the mentioned and other features and advantages. A related object is to do so providing a "multi-path to data" capability in a disk drive, converting "Hard" failure thereof to "Soft" failure. A related object is to do this using "cross-coupling" of actuator control stages. Another object is to do so providing multiple-transducer per track capability. Yet a further object is to teach the use of such modules with independent multiple transducer control whereby transducers can be operated independent and in parallel (e.g., one engaged in "read/write" while one or several others are "seeking" their next read/write address; or some heads positioned over oft-used tracks while others "seek" randomly).
Another object is to do so providing "multiple paths to data" (multi-port flexibility), with multiple transducer assemblies arranged to cover the same addresses, at least in "emergency mode" (and/or in an "assist mode").